[project @ 1999-05-05 08:31:00 by sof]

Allow record pattern "F{}" on any old constructor, not just with those
that have labelled fields.

ghc/compiler/deSugar/Match.lhs

@@ -460,12 +460,22 @@ tidy1 v (LazyPat pat) match_result
 tidy1 v (RecPat data_con pat_ty tvs dicts rpats) match_result
   = returnDs (ConPat data_con pat_ty tvs dicts pats, match_result)
   where
-    pats 	     = map mk_pat tagged_arg_tys
+      {-
+        Special case to handle C{}, where C is a constructor
+	that hasn't got any labelled fields - the Haskell98 report
+	doesn't seem to make that constraint (not that I think it
+	should).
+	-- sof 5/99
+      -}
+    pats
+       | null con_flabels = map (WildPat) con_arg_tys'
+       | otherwise	  = map mk_pat tagged_arg_tys
 
 	-- Boring stuff to find the arg-tys of the constructor
     (_, inst_tys, _) = splitAlgTyConApp pat_ty
     con_arg_tys'     = dataConArgTys data_con inst_tys 
-    tagged_arg_tys   = con_arg_tys' `zip` (dataConFieldLabels data_con)
+    con_flabels      = dataConFieldLabels data_con
+    tagged_arg_tys   = con_arg_tys' `zip` con_flabels
 
 	-- mk_pat picks a WildPat of the appropriate type for absent fields,
 	-- and the specified pattern for present fields